Hi All,I was hoping one of you might be able to help me reconcile some 70E articles. Article 130.7(C)(1) states "When an employee is working within the arc flash boundary......All parts of the body inside the arc flash boundary shall be protected." 130.7(C)(7)(b) goes on to say "Hand and arm protection shall be worn where there is possible exposure to an arc flash burn". 130.5(B)(1) states "The arc flash boundary shall be the distance at which the incident energy equals 5J/cm2 (1.2 cal/cm2)." Labels still in place at many sites appear to only call out for arc-rated FR if the incident energy level equals or exceeds the 1.2 cals at the chest and if less called for the cat 0 non arc rated protection. See the following labels.

Attachment:

IMG_4077.JPG

Attachment:

IMG_4079.JPG

Assuming that if the incident energy at the chest was less than but close to the 1.2 cals it would seem likely that the forearms would easily exceed the 1.2 cal value. Informational Annex H3 states that for cal ratings >1.2 cals Arc Rated garments are needed. Finally 130.5(C)(1) states "Recognizing that incident energy increases as the distance from the arc flash decreases, additional PPE shall be used for any parts of the body that are closer than the distance at which the incident energy was determined."

How should I relate to all this? Assuming that the workers hands are within the 12" restricted approach boundary requiring insulated gloves with the leather protectors the only part of the hand arm that might be at risk of burn would be the forearms. Does the 70E standard by the articles sited then require an FR shirt so the arms are protected assuming the incident energy is greater than 1.2 cals?

For a final thought on this matter I do believe a cotton shirt does provide a significant degree of protection at energy levels not significant enough to ignite the fabric. You can see in the following picture where the single layer of cotton from the workers T shirt made the difference on parts of his neck between a bad burn and no burn at all.

Attachment:

Non FR Protection.jpg

Thanks in advance for any of your thoughts on this matter.Jerry

You do not have the required permissions to view the files attached to this post.

What you are attempting to do is to approach this with a scientific approach. As you dig deeper into the current "incident energy" hazard estimation, you will find more and more very blatant and obvious discrepancies. What we really have at this point is a completely and utterly flawed model for predicting an injury that however flawed it may be, has worked for over a decade. So essentially the best approach at this point is a leap of faith approach.

A statement from Hugh Hoagland explaining this seeming contradiction (reference below) is the following:"Clothing ignition was a primary cause of seriousburn injuries and fatalities for electrical workers exposed to an arc fl ashevent. The adoption of FR clothing for electrical workers by many utili-ties and industrial companies resulted in a signifi cant reduction in arc fl ashburns and fatalities (Bureau of Labor Statistics, 2012 ). Privette continuedthe work for the next 3 years as he investigated and published a criticalstudy on arc fl ash and skin response (previous studies had been done onIR lamps and fl ame sources (see Stoll and Chianta, 1969 ). Privetteâs unpub-lished study showed much promise; however, a lack of funding caused thestandards committees to default to the Stoll Curve (Stoll and Chianta, 1969 )which has been the line of demarcation for clothing and equipment arc rat-ings since it characterizes the âonset of second degree burnâ. It is not true, assome of the standards indicate, that the worker has a probability of a seconddegree burn at the arc rating. The fact is that many workers do not receiveany burns. The number/curve is a theoretical model."

As to the arms vs. chest/face, it's quite simple. What most people fail to recognize is that the whole thing is based on survival. You can survive without you arms and legs but a burn in the chest/face area significantly reduces the chances for survival. 70E is not based on "no injury" or "just curable" or anything like that except in the critical areas of the body...it's only meant as a survival standard. It's a survival standard. This should be pretty obvious but the incident energy increases as you get closer to the arc. It is simply physically impossible to provide PPE that can survive the arc and still retain any use of the hands and arms if we tried to do this. Imagine what ATPV 300 would look like on your hands. Obviously the whole standard is a joke from this point of view since when we say "8 cal/cm2", we mean uniform 8 cal/cm2 for all points on the body. The legs and back should be a little less in most cases while the hands and arms should be much higher but going back to Hoagland's statements...this is a theoretical concept, not a practical one. Any attempt at understanding it from an engineeering perspective will fail.

Delving somewhat deeper your argument about cotton shirts and the like is VERY accurate. There have been some papers published discussing this exact thing. Simply put, either the material itself or the chemical treatment applied to the fabrics to make them "FR" prevents them from sustaining a flame. The insulative value (ATPV) is entirely due to their ability to thermally insulate..usually by trapping air. An ordinary untreated cotton fabric does indeed work up to around 10 cal/cm2 or more as long as it doesn't ignite. Various "meltable" fabrics such as nylon and polypropylene do an even better job of insulating, as long a they don't melt or ignite.

Here are some references on the subject, although the first one is probably the best in terms of giving you the information you are looking for. All three look at the ignition point (ATPV) of cotton and similar materials but the first one looks at incident energy of a worker protected by untreated cotton as well. I know none of these are free but you can find them in a local college library.

The upshot of the latter is that yes even if the incident energy is just under 1.2 cal/cm2, there is a chance that a cotton shirt could ignite and cause a pretty severe burn. The alternative is to wear FR PPE for effectively ALL electrical work, no matter what the incident energy rating is. That is almost exactly what OSHA has put out as a regulatory requirement for utility workers.

In a chapter entitled "Flame resistance textiles for electric arc flash hazards" penned by Hugh Hoagland, he had this rather interesting statement: "Arc fl ash standards, in contrast, allow only a 50% probabilityof onset of second degree burn in the area that the arc hits. In practice, thismeans <25% body burn in a real life incident because of the focused natureof arc fl ashes in the fi eld. Even the arc fl ash tests ASTM F1959, IEC 61482-1-1 and IEC 61482-1-2 do not cover more than the area of the front of ashirt with the arc fl ash energy. When clothing does not ignite or melt, reallife incidents rarely result in more than 25% of the body being exposed inan arc fl ash event."

I can't find the reference for you right now but another interesting point is that FR PPE prevents propagation of a flame and that the area of exposure is "focussed" on an area less than 25% of the body. A lot of burn data shows that if burns are confined to less than 25% of the body's total surface area, survivability is extremely good. The upshot is that even if the PPE is completely under-rated, wearing non-combustible PPE (in other words, FR rated PPE) virtually guarantees survival. In other words the case you are describing is covered by wearing FR PPE. Even more importantly to me personally even if I'm dealing with say a 20 cal/cm2 incident energy condition and I'm wearing only 10 ATPV PPE, I have a very high chance of survival.

I've been at odds for years with Hugh Hoagland's idea that essentially all electrical workers should be in FR PPE for almost every task. My arguments are that first off it seems kind of pointless to be wearing it for "marginal cases" like <1.2 cal/cm2 and in years past, the stuff was downright uncomfortable and only something I would wish on a welder. But I've softened a lot on my opinion. Based on some of Hugh's claims it seems more likely that survival is all but guaranteed with any level of FR PPE, no matter what the ATPV and incident energy. That's extremely comforting to know. Then if we want to argue about how much PPE should be worn above this very basic baseline of protection and refine it a little as long as we don't do stupid things and go crazy with the requirements, I'm all for that, too.

What changed? A couple things. First and foremost, I worked in a foundry for 5 years. I was in FR PPE during the entire work day, every day. Second I observed the arguments, frustrations, and difficulties that a large national lineman contractor had with switching to requiring FR PPE. There was resistance at first but it seems to have finally become accepted. The final issue is that many areas and operations require hi visibility PPE in addition or in lieu of FR PPE. In years past the choices were either/or but not both. More recently you could start to get hi vis vests that were Glengard or something similar that is both hi vis and FR PPE. It is mostly modacrylic for color fastness and it is VERY expensive, especially because Glengard is patented. The alternative is FR rain suits that are not only not very comfortable (they don't breathe at all) but very expensive. However now Glengard or something similar can be purchased as rolls of stripes and a lot of vendors now offer an ordinary FR shirt with FR stripes sewn onto the shirt. That has basically eliminated the problem although if I could just find knit long sleeve FR hi vis T-shirts for around $30 I'd be buying them and wearing them instead, especially here in the South in the summer when full long sleeve 12 oz twill shirts are very hot and sticky to wear.

Bringing it home, this is not just an engineer spouting some kind of opinion here. If you see me on a service call that involves energized equipment today, I have on a tan shirt ATPV 10 and either brown duck pants or blue twill pants on, both with ATPV 12. A lot of the time since many of my customers can't afford full time electricians never mind engineers, they have no idea what the incident energy of their equipment is and neither do I. So I might be over or under-rated but there's not much I can do about it except dig out the 40 cal suit when I know that I'm dealing with something where the incident energy is even higher....I use the much maligned tables.

Switching to FR PPE is easy in a steel mill or foundry, or a refinery, or pipelines, or some coal mines because that has been the rule for years, and more recently for utilities. It is a much bigger leap of faith for everyone else. So I can understand and respect the idea that FR PPE is not and should not be mandatory for all workers in all cases. We're talking about an extremely unlikely injury in the first place. For instance I can't possibly justify making every residential electrician wear FR PPE. Nor could I make the case for the vast majority of relaying or controls technicians that rarely work above 120 V equipment. But for the rest of us, it should be given serious consideration.

Hi Paul and thank you as always for your thoughtful thought out response. What I gleaned from it was that as I had suspected the arms are at risk of experiencing incident energy at levels above the 1.2 cal limit even though the IE at the working distance is less than the 1.2 cal level. There was one more 70E article that I should have sited in my first post, article 130.7(C)(6), it says "Employees shall wear arc-rated clothing wherever there is possible exposure to an electric arc flash above the threshold incident energy level for a second degree burn......1.2cal/cm2." With this in mind if someone were to attempt to follow 70E to the letter than wouldn't they have to do an incident energy calculation at the distance from the arc source where the rubber insulated glove with its leather protector ends? This is even making an exception for the gloves in that they are not arc rated. If this study showed the arms to be above the 1.2 cal limit than wouldn't arc rated FR be required per the standard? I feel sometimes like I am taking these quest for understanding to the point of absurdity but as someone who does training I know at some point in time the question will be asked and I like to feel somewhat prepared to answer. If I am reading the standard and interpreting your comments correctly many of these pieces of equipment with the older labels indicating an HRC cat. of "0" or newer installations where the labels indicated no arc rated FR needed are probably not in compliance with 70E, at least its' article 130.7(C)(6).Jerry

There was one more 70E article that I should have sited in my first post, article 130.7(C)(6), it says "Employees shall wear arc-rated clothing wherever there is possible exposure to an electric arc flash above the threshold incident energy level for a second degree burn......1.2cal/cm2." With this in mind if someone were to attempt to follow 70E to the letter than wouldn't they have to do an incident energy calculation at the distance from the arc source where the rubber insulated glove with its leather protector ends? This is even making an exception for the gloves in that they are not arc rated. If this study showed the arms to be above the 1.2 cal limit than wouldn't arc rated FR be required per the standard?

You're not going to get there. Rubber gloves have been type tested and generally somewhere in the 40-50 cal/cm2 range. At some point along the rubber glove as you get closer to the finger tips, we'll end up above 40 cal/cm2. That's not the way that 70E (and really IEEE 1584 that the vast majority of 70E is based on) works. It's a theoretical model. We calculate incident energy at a single point and base PPE on that one and only point.

Quote:

I feel sometimes like I am taking these quest for understanding to the point of absurdity but as someone who does training I know at some point in time the question will be asked and I like to feel somewhat prepared to answer. If I am reading the standard and interpreting your comments correctly many of these pieces of equipment with the older labels indicating an HRC cat. of "0" or newer installations where the labels indicated no arc rated FR needed are probably not in compliance with 70E, at least its' article 130.7(C)(6).

Keep in mind 2 things:1. IEEE 1584, ASTM 1959, and thus 70E are about survivability. No attempt is being made to prevent injuries. IEEE 1584 even makes this more clear when there is a table showing that using the empirical equations and wearing PPE according to ASTM 1959, it fails to provide adequate protection 10% of the time (that is avoiding burns to the face and chest). No attempt is made to protect anything other than vital areas.2. IEEE 1584 is a purely theoretical model. You can't read anything into it. The PPE recommendations in 70E and based on IEEE 1584 are based on a theoretical model. It has no basis in reality. It works really good according to historical evidence though so we stick with it. Even though it is flat out wrong, employees are still going to walk away. They might be injured, maybe even have severe burns, but they will survive. That's all that 70E promises. So we wear PPE rated according to ASTM 1959 or related standards, UNIFORMLY, using a totally empirical equation and it works very well, even if the theory is crap.

Having done training myself, you can see the obvious and glaring problem here. Generally if you are training electricians, you are usually dealing with the very best and brightest out of any particular group. They will see right through the smoke and mirrors. Ultimately we are asking this crowd to take a leap of faith and arguments as to the validity and value of 70E need to be made based on a track record of success, not analyzing the finer points because it will fail the latter every time. I realize that this is a bit unsettling. It certainly flies in the face of engineers but it's all we have to date.

Doan collected about 40 cases from DuPont. In cases where no arc flash protection was implemented, serious injuries were 90%. With 70E tables (the original pre 2015 version), it was 50%. When IEEE was followed, 0% injuries. I know of no other cases where IEEE 1584 "failed" including below 1.2 cal/cm2. There has been a single case in 2009 of a 240 V arc flash fatality so it is possible down to that level but I haven't seen any evidence except to the contrary supporting self sustaining arcs at 120 V.

Forgot to mention. OSHA has documented a couple 120 V injuries involving hospitalization. In one case the cord for a laptop failed. In the other a permanently mounted gang receptacle type of thing had a loose metal cover and it caused an arc at 120 V which resulted in a hand injury. Both of these are definitely "office equipment" and well below the threshold that NFPA 70E covers...as I said, it's a survival standard, not a "no injuries" standard.

Who is online

Users browsing this forum: No registered users and 2 guests

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum